Removal of phosphate compounds from fluoride containing solutions

ABSTRACT

A process for removing phosphate compounds such as phosphoric anhydride (P2O5) from fluoride containing solutions such as dilute hydrofluoric acid (HF) or fluosilicic acid (H2SiF6) is disclosed. This process involves the precipitation of aluminum phosphate (AlPO4) from the acidic fluoride containing solutions. The precipitation is brought about by the addition of an aluminum salt such as aluminum fluoride (AlF3), aluminum chloride hydrate (AlCl3.6H2O), aluminum nitrate (Al(NO3)3.9H2O), aluminum sulfate (Al(SO4)3.13-1/2H2O), aluminum ammonium sulfate (Al2(SO4)3.(NH4)2SO4.24H2O) and triammonium aluminum hexafluoride ((NH4)3AlF6). The pH is then adjusted to at least about 3 and the phosphoric anhydride is removed by precipitation.

1 1 Mar. 11,1975

i 1 REMOVAL OF PHOSPHATE COMPOUNDS FROM FLUORIDE CONTAINING SOLUTIONS [76] Inventor: Gustave E. Kidde, 201 South Lake Avenue, Pasadena, Calif. 91101 22 Filed: Mar. 26, 1973 21 Appl. No.: 345,112

Related U.S. Application Data [63] Continuation of Ser. No. 89,126, Nov. 12, 1970,

abandoned.

{52] U.S. Cl 423/484, 423/341, 423/472,

423/483, 423/488 [51] Int. Cl...... C0lb 7/22, COlb 7/0O,C01b 33/00 FOREIGN PATENTS OR APPLICATIONS 1,095,859 12/1967 Great Britain 423/341 Primary Examiner-Edward Stern Attorney, Agent, or Firm-Lyon and Lyon [57] 5 ABSTRACT A process for removing phosphate compounds such as phosphoric anhydride (P 0 from fluoride containing solutions such as dilute hydrofluoric acid (HF) or fluosilicic acid (H SiF is disclosed. This process involves the precipitation of aluminum phosphate (Al- PO from the acidic fluoride containing solutions. The precipitation is brought about by the addition of an aluminum salt such as aluminum fluoride (AlF aluminum chloride hydrate (AlC1 .6I-l O), aluminum nitrate [AI(NO .9H O], aluminum sulfate [Al(- SO .13-l/2H O], aluminum ammonium sulfate [Al- (SO .(NH SO .24H O] and triammonium aluminum hexafluoride [(NH AIF The pH is then adjusted to at least about 3 and the phosphoric anhydride is removed by precipitation.

11 Claims, N0 Drawings REMOVAL OF PHOSPHATE COMPOUNDS FROM FLUORIDE CONTAINING SOLUTIONS This is a continuation of application Ser. No. 89,126, filed Nov. 12, 1970, now abandoned.

BACKGROUND OF THE INVENTION The field of the invention is inorganic chemistry and more specifically relates to processes for utilizing fluorine containing compounds in solution. One such use of fluorine containing compounds in solution is the production of synthetic cryolite (Na AlF from dilute solutions of hydrofluoric acid. One such process is disclosed in applicants application Ser. No. 802,274 filed Feb. 25, 1969 and now US. Pat. No. 3,556,717, issued Jan. 19, 1971, which is incorporated by reference herein to illuminate the background of the present invention. The presence of dissolved phosphoric anhydride in these fluorine containing solutions makes them unsuitable for further processing to useful compounds such as synthetic cyrolite or aluminum fluoride.

The manufacture of phosphoric acid, diammonium phosphate, triple super phosphate and other phosphatic chemicals from phosphate rock and sulfuric acid produces fluosilicic acid (H SiF as a by-product. This by-product fluosilicic acid contains varying amounts of dissolved phosphoric anhydride (P This dissolved phosphoric anhydride prevents the further use of the fluosilicic acid in the production of aluminum fluoride or synthetic cryolite. Further, dilute solutions of hydrogen fluoride are produced in the thermal process of defluorinating phosphate rock for use as a cattle feed supplement. This hydrofluoric acid solution contains dissolved phosphoric anhydride which constitutes a phosphate contaminant making the solution unsuitable for further processing to aluminum fluoride or synthetic cryolite.

SUMMARY It has been discovered that phosphate contaminants such as dissolved phosphoric anhydride (P 0 may be removed from fluorine-containing solutions such as fluosilicic acid and dilute hydrofluoric acid solutions. This removal can be brought about by the addition of an aluminum salt followed by an adjustment of the pH to about 3.0. This results in a precipitation which is removed from the solution leaving fluoride containing solutions which may be readily processed to aluminum fluoride, synthetic cryolite or the like by accepted procedures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS It is believed that the addition of aluminum containing compounds to solutions which contain phosphate contaminants such as phosphoric anhydride (P 0 results in a precipitation in the form of aluminum phosphate (AIPO Any aluminum containing compound of sufficient solubility may be used in the practice of the present invention. We have found the following aluminum salts to be particularly effective: Aluminum fluoride (AlF aluminum chloride hydrate (AlCl .6- H O), aluminum nitrate [Al(NO .9H,O], aluminum sulfate [Al(SO l 3%H O], aluminum ammonium sulfate [Al (SO .(NH ),SO .24H,O] and triammonium aluminum hexafluoride [(NH AlF The effectiveness of phosphate removal is dependent upon proper pH control and it has been found that a minimum pH between 2.6 and 3.1 results in essentially complete removal of phosphoric anhydride (P 0 Since the fluoride containing solutions tend to be highly acidic it is usually necessary that neutralization agents be added to bring the solution to the proper pH. The choice of neutralization agents is not critical and is dependent upon solubility and economic considerations. The following materials have been successfully used: Ammonia, sodium hydroxide, sodium carbonate, potassium carbonate and potassium hydroxide.

The colorimetric analysis for phosphoric anhydride in a medium containing fluorine and silica requires the removal of both of these constituents prior to colorimeter determination for phosphoric anhydride content. This may be done by taking a sample to dryness and then fuming with hydrogen fluoride to remove silica (SiO followed by treatment with perchloric acid (HClO for fluorine removal. The remaining phosphoric anhydride is then determined by the molybdatestannous chloride method. The percentage transmittance at 650p. was determined for known solutions of phosphoric anhydride. A curve was then drawn which was then later used to determine phosphoric anhydride concentration. The following transmittance results were used to form a basic curve for colorimetric determination of phosphoric anhydride:

P 0 Concentration Transmittance Grms/IOO ml. at 650p.

The present invention can be more fully understood by reference to the illustrative examples which follow.

EXAMPLE I TABLE NO. 1

ALUMINUM FLUORIDE ADDITION Filtrate Grs. Grs. P 0 AlF Aqua pH Grams P 0 1.93 4.5 3L9 6.3 [85.5 0.002 L93 4.5 35.9 7.4 169.5 0.0005 1.93 4.5 39.9 7.4 l86.7 nil 1.93 4.5 43.9 7.5 l72.0 nil 1.93 4.5 2 5.8 2.0 186.5 0.3 1.93 4.5 28.8 3.0 221.4 nil 1.93 4.5 3 l .2 4.0 209.7 nil 1.93 4.5 34.8 5.0 217.8 nil EXAMPLE 2 TABLE NO. 3-Continued The above procedure was repeated except that trlam- ALUMINUM CHLORIDE ADDITION momum hexafluonde was subst1tuted for the alumlnum Acid fluoride of Example 1. The results are shown in Table Sample 3 NO. 2 below: a -i P205 611 0 Aqua 22 L8 249.9 0.003 100 107.7 TABLE NO. 2 23 1.8 240.8 0.001 100 108.5 24 1.8 221.4 nil 100 112.0 25 2.0 0.02 REMOVAL OF P205 FROM H SiF SOLUTION 26 3.0 nil USING (NHJ AIF AT 3.0 pH 10 27 4.0 nil Grs. 29% pH Grs. Dry Wgt. Wgt. 28 5.0 nil NH Slurry Cake Filtrate ampl %P2O5 EXAMPLE 4 l5 Alummum n1trate was ut1l1zed as a source of alum1- EXAMPLE 3 num with the following results shown in Table 4. Again,

Aluminum chloride hydrate was successfully used as each Sample contained 200 grams of percent HzsiFs' a source of aluminum to remove varying amounts of P 0 from 15 percent fluorosilicic acid solutions. The TABLE NO. 4 pH was adjusted by ammoniation. Each sample contained 200 grams of 15 percent H SiF The results are ALUMINUM NITRATE ADDITION Acid rs. as follows Sample Grs. AI(NO3);1 Grs. TABLE NO. 3 No. H3PO.1 P205 .9H 0 Aqua 29 1.38 0.49 5.28 27.0 ALUMINUM CHLORIDE ADDlTlON 1 49 5.28 31.0 Add 31 1.38 0.49 5.28 35.0 Sample Grs. Grs. A1c1 Grs. 8 g; 3%: N H PO P 0 6H 0 A o 2 5 qua 34 2.76 0.98 10.56 33.5 30 2.76 0.98 10.56 37.5 5 8'23 3'2} 38 36 5.52 1.93 21.12 31.9 3 37 5.52 1.93 21.12 35.9 4 38 5.52 1.93 21.12 43.9 5 39 8.28 2.86 31.68 34.3 6 1 8.28 2.86 31.68 38.3 7 5 41 8.28 2.86 31.68 42.3 8 35 42 8.28 2.86 31.68 46.3 9 "93 3'64 43 11.04 3.77 42.24 36.7 10 3 44 11.04 3.77 42.24 44.7 H 3'64 39') 13.80 4.63 52.80 39.1 12 [3'64 46 13.80 4.63 52.80 43.1 3 47 13.80 4.63 52.80 47.1 14 48 13.80 4.63 52.80 51.1 15 8.28 2:86 20:46 42:3 40 49 2H2 16 8.28 2.86 20.46 46.3 2H2 17 11.04 3.77 27.28 36.7 lg; 18 11.04 3.77 27.28 40.7 19 11.04 3.77 27.28 44.7 20 11.04 3.77 27.28 48.7 Sample Wash 21 13.80 4.63 34.10 39.1 22 13.80 4.63 34.10 43.1 45 PH 3 3 0 4 34 10 47 29 2.8 227.9 0.000 100 102.2 24 3 0 4 3 34 SL] 30 3.9 220.6 0.004 100 104.1 5 552 L93 1364 2 31 4.8 213.5 nil 100 105.9 26 552 L93 13 4 33 32 6.7 220.2 1111 100 100.0 27 552 1.93 1164 352 33 3.3 221.4 0.011 100 103.0 2 5 52 1 93 3 4 3 0 34 4.3 217.1 0.009 100 116.6 50 35 5.6 215.8 0.009 100 106.4 36 5.2 227.8 0.005 100 121.7 sample F'mme wash 37 5.6 220.6 0.002 100 114.0 0 38 7.1 219.1 nil 100 108.3 P P105 out 39 2.0 242.0 0.002 100 1 13.6 1 2.5 219.1 0.004 100 108.8 40 2.7 228.9 0.001 100 115.1 2 4.6 217.4 nil 100 103.5 41 3.3 227.0 nil 100 111.3 3 5.7 l87.4 nil 100 131.8 42 4.8 219.8 nil 100 113.1 4 6.4 201.1 nil 100 120.3 43 3.0 249.0 0.003 100 120.6 5 2.2 229.4 0.30 100 103.7 44 2.2 234.7 nil 100 106.4 6 2.3 225.8 0.075 100 104.2 45 3.1 248.1 0.001 100 132.7 7 2.6 215.1 0.004 100 103.4 46 2.3 248.5 nil 100 125.8 8 3.5 213.3 nil 100 104.2 47 2.0 244.2 nil 100 122.4 9 L8 240.2 0.02 50 52.0 48 2.0 234.7 nil 100 116.3 10 2.0 224.7 0.01 100 103.5 49 2.0 0.02 11 2.6 208.8 0.007 100 110.4 50 3.0 n1] 12 3.3 209.6 nil 100 108.6 51 4.0 n11 13 1.8 237.1 0.06 100 105.9 2 5.0 n11 14 1.8 220.7 0.01 100 116.2 15 2.1 218.2 nil 100 108.2 16 2.2 200.0 nil 100 110.2 17 2.0 230.7 0.002 100 105.5 18 2.0 229.9 0.002 107.4 EXAMPLE 5 $8 '23 :88 Aluminum sulfate was used as an aluminum source 21 2.0 239.9 0.01 100 113.4 resulting in complete removal of P 0 at a pH of 3.0.

Each sample contained 200 grams of H SiF The results are shown in Table No. 5:

TABLE No. 5

ALUMINUM SULFATE ADDITION Grams Grams Sample Grs. 100% Al (SO Aqua No. H PO P l3 H O NH Filtrate Samp No. pH Grms. P 0 53 2.0' 228 0.04 54 2.5 226 0.01 55 3.0 229 nil 56 2.0 220 0.03 57 2.5 211 0.02 58 3.0 223 nil 59 2.0 230 0.004 60 2.5 220 0.003 61 3.0 223 nil 62 2.0 240 0.002 63 2.5 226 0.002 64 3.0 224 nil EXAMPLE 6 TABLE No. 6

P 0 REMOVAL FROM DILUTE HF USING ALUMINUM SALTS AND AMMONIA 2.0 3.0 4.0 5.0 A1 Salt Used Grms. pH pH pH pH AlCl .6H 0 10.5 0.05 nil nil nil A1(NO .9H O 16.0 nil nil nil nil AIF 3.7 0.01 nil nil n11 (NH.,);A1F,, 8.5 0.05 0.003 nil nil Al(SO,) 13%H O 12.5 0.02 0.003 nil nil From the foregoing specifications and examples it can be seen that many variations of the present invention are possible. A primary feature of the invention is the removal of phosphate contaminates from acidic fluoride solutions which treated solutions can then be utilized for further processing to useful chemicals. The reactions are carried out at ambient conditions of temperature and pressure. The reaction rates are such that the precipitate is formed without undue delay and no heating is required. The solubility of the resulting aluminum phosphate precipitate is such that no additional cooling is required to assure essentially complete removal of phosphoric anhydride. The reaction may thus be simply carried out in unheated equipment at atmospheric pressure. The precipitate is readily removed by settling or filtration. Other aluminum salts having sufflcient solubility may be used in place of the aluminum salts disclosed. Adjustment of pH may be carried out by the addition of other bases than the ones disclosed above as long as their solubility is sufficient and they do not themselves constitute a contaminant for further processing of the fluoride solution. Thus, it can be seen that the foregoing examples and specification are merely illustrative examples of the invention and should not be taken as limiting the scope of the present invention because it is Applicants intent that the scope of the present invention be limited only by the lawful scope of the claims which follow.

I claim:

1. A process for the removal of phosphate contaminants from impure fluosilicic acid and hydrofluoric acid aqueous solutions having a pH of less than 2.6 comprising:

adding to said solution a water soluble aluminum salt in an amount sufficient to precipitate. any phosphate contaminants as aluminum phosphate; decreasing the acidity of said solution to a pH of at least 2.6 to 3.1; and separating the resulting precipitate from the resulting phosphate contaminant free solution. 2. The process of claim 1 wherein said water soluble aluminum salt is AlFg.

3. The process of claim 1 wherein the aluminum salt is AICI .6H O.

4. The process of claim 1 wherein the aluminum salt is Al (SO .l3 /zH O.

5. The process of claim 1 wherein the aluminum salt is AI (SO .(NH SO .24H O.

6. The process of claim 1 wherein the aluminum salt is (NH AlF 7. The process of claim 1 wherein said solution is neutralized by ammoniation.

8. A process for the removal of phosphoric anhydride from aqueous solutions of acidic fluorine containing compounds selected from the group consisting of fluosilicic acid (H SiF and hydrofluoric acid (HF) said solution having a pH of less than 2.6 comprising:

adding a water soluble aluminum salt to said solutions in an amount sufficient to precipitate any phosphoric anhydride as aluminum phosphate, said salt being selected from the group consisting of aluminum fluoride (AlF aluminum chloride hydrate (AlCl .6H O), aluminum nitrate [Al(NO .9- H O], aluminum sulfate [Al(SO .l3 /2H O], aluminum ammonium sulfate [Al (SO .(NH SO .24H O] and triammonium aluminum hexafluoride [(NHQ AIF decreasing the acidity of said solution to a pH of at least about 3: and

separating the resulting precipitate from the resulting purified solution.

9. The process of claim 8 wherein the pH is adjusted by the addition of ammonia.

10. A process for the removal of phosphoric anhydride from aqueous solutions of acidic fluorine containing compounds selected from the group consisting of fluosilicic acid (H SiF and hydrofluoric acid (HF) said solution having a pH of less than 2.6 comprising:

adding aluminum fluoride (AIF in an amount sufficient to precipitate any phosphoric anhydride as aluminum phosphate;

decreasing the acidity of said solution to a pH of at least about 3; and

separating the resulting precipitate from the resulting purified solution.

11. The process of claim 10 wherein the pH is adjusted by the addition of ammonia. 

1. A PROCESS FOR THE REMOVAL OF PHOSPHATE CONTAMINANTS FROM IMPURE FLUOSILICIC ACID AND HYDROFLUROIC ACID AQUEOUS SOLUTIONS HAVING A PH OF LESS THAN 2.6 COMPRISING: ADDING TO SAID SOLUTION A WATER SOLUBLE ALUMINUM SALT IN AN AMOUNT SUFFICIENT TO PRECIPITATE AN PHOSPHATE CONTAMINANTS AS ALLUMINUM PHOSPHATE; DECREASING THE ACIDITY OF SAID SOLUTION TO A PH OF AT LEAST 2.6 TO 3.1; AND SEPARATING THE RESULTING PRECIPITATE FROM THE RESULTING PHOSPHATE CONTAMINANT FREE SOLUTION.
 1. A process for the removal of phosphate contaminants from impure fluosilicic acid and hydrofluoric acid aqueous solutions having a pH of less than 2.6 comprising: adding to said solution a water soluble aluminum salt in an amount sufficient to precipitate any phosphate contaminants as aluminum phosphate; decreasing the acidity of said solution to a pH of at least 2.6 to 3.1; and separating the resulting precipitate from the resulting phosphate contaminant free solution.
 2. The process of claim 1 wherein said water soluble aluminum salt is AlF3.
 3. The process of claim 1 wherein the aluminum salt is AlCl3.6H2O.
 4. The process of claim 1 wherein the aluminum salt is Al2(SO4)3.13- 1/2 H2O.
 5. The process of claim 1 wherein the aluminum salt is Al2(SO4)3.(NH4)2SO4.24H2O.
 6. The process of claim 1 wherein the aluminum salt is (NH4)3AlF6.
 7. The process of claim 1 wherein said solution is neutralized by ammoniation.
 8. A process for the removal of phosphoric anhydride from aqueous solutions of acidic fluorine containing compounds selected from the group consisting of fluosilicic acid (H2SiF6) and hydrofluoric acid (HF) said solution having a pH of less than 2.6 comprising: adding a water soluble aluminum salt to said solutions in an amount sufficient to precipitate any phosphoric anhydride as aluminum phosphate, said salt being selected from the group consisting of aluminum fluoride (AlF3), aluminum chloride hydrate (AlCl3.6H2O), aluminum nitrate (Al(NO3)3.9H2O), aluminum sulfate (Al(SO4)3.13- 1/2 H2O), aluminum ammonium sulfate (Al2(SO4)3.(NH4)2SO4.24H2O) and triammonium aluminum hexafluoride ((NH4)3AlF6); decreasing the acidity of said solution to a pH of at least about 3: and separating the resulting precipitate from the resulting purified solution.
 9. The process of claim 8 wherein the pH is adjusted by the addition of ammonia.
 10. A process for the removal of phosphoric anhydride from aqueous solutions of acidic fluorine containing compounds selected from the group consisting of fluosilicic acid (H2SiF6) and hydrofluoric acid (HF) said solution having a pH of less than 2.6 comprising: adding aluminum fLuoride (AlF3) in an amount sufficient to precipitate any phosphoric anhydride as aluminum phosphate; decreasing the acidity of said solution to a pH of at least about 3; and separating the resulting precipitate from the resulting purified solution. 